The goal of this research is to increase the clinical utility of the CEA assay for diagnosis and monitoring of malignant disease, particularly cancer of the large bowel. The approach being used is to define CEA chemically and to identify distinctive portions of the molecule against which antisera can be prepared. Since research in our laboratory strongly supports the idea that the antigenic activity of the CEA molecule resides in the protein chain, particular attention is being given to determining its structure. Techniques have been established for the enzymic cleavage of this highly glycosylated molecule and the separation of the resultant glycopeptides by high pressure liquid chromatography with sufficient purity to permit amino acid sequencing. Techniques for the deglycosylation of CEA and for subsequent cleavage into specific peptides are being developed. CEA related molecules possessing similar but distinctive protein chains have been identified and play a key role in this study.